I think cherokeesam is right in every word. It amazes me how some people don't see why it's not a GotG and Avengers "crossover". Just read all his points, it's very simple and logical.

I honestly highly believe it's Spider-Man in the MCU. Perhaps that will affect ASM4 as well.

I think so, too.
All the pieces add up:

a Sony-Marvel merger that would allow Spidey into the MCU has been discussed constantly (case in point....) even from the Raimi days;

it's definitely "something big";

it would definitely fit the "kinda like a merger of brands" criteria;

Sony and Marvel both have long said they're amenable to a crossover, and there were even plans to include Stark Tower in the TASM skyline;

Vin talked about being in a "new IP" for 2016, and Daredevil seems like a reasonable candidate for one of those coveted slots;

Feige said something awhile back about a major event in the MCU in 2017, and even back then a lot of speculation swung towards Spider-Man;

Vin Diesel as Kingpin makes perfect sense ---- hell, imho, it's the role he was born to play;

Vin has stated that he wanted to play a villain in Marvel instead of a hero;

and Kingpin is the ideal connector between a Sony property (TASM) and a Marvel one (DD).

Marvel *needs* to roll out their Marvel Knights, their street-level heroes. I've always said Marvel Studios should create a smaller substudio --- i.e., "Marvel Knights" --- to handle smaller-budget properties like Daredevil, Elektra, Moon Knight, Luke Cage, Iron Fist, Blade, Punisher, and Ghost Rider; and adding Spider-Man to the mix....well, that's where the rubber meets the road. They *belong* together....a street level sub-MCU that operates in the same universe as the Avengers and the cosmic heroes and villains, while still keeping them as separate as they more or less are in the actual comic-book universe.